Gas turbines typically comprise several interconnected discrete parts. A gas turbine generally includes an inlet section, a compression section, a plurality of combustors, a turbine section, and an exhaust section. The inlet section may include a series of filters, cooling coils, moisture separators, and/or other devices to purify and otherwise condition a working fluid (e.g., air) entering the gas turbine. The working fluid flows downstream from the inlet section to a compressor section where kinetic energy is progressively imparted to the working fluid to produce a compressed working fluid at a highly energized state. The compressed working fluid is mixed with a fuel from a fuel supply to form a combustible mixture within one or more combustors. The combustible mixture is burned to produce combustion gases having a high temperature and pressure. The combustion gases flow through a turbine of a turbine section wherein energy (kinetic and/or thermal) is transferred from the combustion gases to rotor blades, thus causing a shaft to rotate and produce work. For example, the rotation of the turbine shaft may drive the compressor to produce the compressed working fluid. Alternately or in addition, the shaft may connect the turbine to a generator for producing electricity. Exhaust gases from the turbine flow through an exhaust section that connects the turbine to an exhaust stack downstream from the turbine. The exhaust section may include, for example, a heat recovery steam generator for cleaning and extracting additional heat from the exhaust gases prior to release to the environment.
The combustors of a gas turbine are generally coupled to the inlets of a first stage nozzle of the turbine section via transition ducts. Typically, each transition duct has an aft frame positioned adjacent to an inlet of the turbine section. The aft frame will usually have two arcuate portions which are typically referred to as inner and outer portions, being inner and outer in the radial direction with respect to the centerline axis of the turbine. The inner and outer portions of the aft frame are interconnected by radially extending linear portions, often referred to as side portions. Inner and outer circumferential seals are used to seal between the inner and outer portions of the aft frame and the corresponding inlet of the turbine section. Radially oriented side seals can be disposed between adjacent aft frames to substantially close and seal off the circumferential gaps between the side portion of one aft frame and the next aft frame.
The radially oriented side seals between circumferentially adjacent aft frames are axially offset (with reference to the turbine axis) from the inner and outer seals between each aft frame and the inlet. Because of this axial offset, gaps remain between the inner and outer seals and the side seals. Gas turbines usually burn hydrocarbon fuels and produce air polluting emissions such as oxides of nitrogen (NOx) and carbon monoxide (CO). Thus, gaps between the inner and outer seals and the side seals may lead to escape of working fluid (e.g., compressed air and/or combustion gases) flowing through the transition duct from the combustor to the first stage nozzle, which can cause lower performance and a shift in the emission of air pollutants.